What quantity is measured by a battery rating given in ampere-hours c+wjv7u-c bwzd nprg)11d+ u2$(A\cdot H)$ ?

When an electric cell is connected to a cirj u pb/8h0qt,n7vvgmz4l 4xklyb+ ( s8cuit, electrons flow away from the negative terminal yn+ lxjbgv4qh7plkb8 04mt v(,sz/8u in the circuit. But within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being used up: battery current, )ppqg3 a l( hfurv-sfrvn4hz-,)d. :ebattery voltage, battery energy, battery power,( :du4vv-a)rs.pqf g,nr h elp-)zf3h or battery resistance? Explain.

One terminal of a car battery is said to be connected to “ground.” Since it is(nk/f: a lvwt7 uq(;hazt5 4ze not really connected to the ground, what is meant by this expressioae;l/twq( v7tau f:45zzh( knn?

When you turn on a water faucet, the water usut;jw19* w2 jgqw3 xfzmally flows immediately. You don’t have to wait for water to flow fro3;g wwft2jjq1 9 *xwmzm the faucet valve to the spout. Why not? Is the same thing true when you connect a wire to the terminals of a battery?

Can a copper wire and an aluminum wire of the same length have the same resisj29mp3fkw0u/pg *e j :ddz s.xtance? E3pd9j/z2 *s mujx0f:pgwek .dxplain.

If the resistance of a small immersion heater (to heat wa/se/dtk ltgp8:u1:f5,r y re ki:okq4 ter for tea or soup, Fig. 18–32) was increased, woiq:s, /teplr8o1f: krue:tg5kd yk/ 4uld it speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon has8m+nog;nx0 x j sides of lengths a, 2a, and 3a, how would you connect the jx +g; n0mnxo8wires from a battery so as to obtain (a) the least resistance, (b) the greatest resistance?

The equation $P\,=\,V^2/R$ indicates that the power dissipated in a resistor decreases if the resistance is increased, whereas the equation $P\,=\,I^2/R$ implies the opposite. Is there a contradiction here? Explain.

What happens when a ligh)6 lmiu/kze0ge,a m1utbulb burns out?

Explain why lightbulbs almost always burn out just as /eah8y /jz:gd. u pru- ro 2i,(jj1aqsthey are turned on and not after they havoau rp2hejyi /-j(/.,u1:qz 8asjdgre been on for some time.

Which draws more current, a 100-W c-jx 2ebb,h p;hy +yi7lightbulb or a 75-W bulb? Which has the higher resistaj- +7xcipb hhbe2y,;ynce?

Electric power is transferred over large distances at very high voltages. Explp tv)q5bbat2 8ain how the high voltage reduces powe2abtbp5v )qt8 r losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replace this fuse with a ;2 ye6r b bew jf v6zzl34u29dj4rzys425- 9l4y zersr4vjzyedb 263 4bwfu2j6 z;A fuse?

When electric lights are operated on low-frequ-/ac*ef 9 7wpjk;krn mency ac (say, 5 Hz), they flicker noticeably. Wh9j ekkfwc7*/a-;pmr ny?

Driven by ac power, the same electrons pass backa/ rk( gwvg(7crm8o1b and forth through your reading la o wkb8c(gva7(1r gm/rmp over and over again. Explain why the light stays lit instead of going out after the first pass of electrons.

The heating element in a toaster is made of Nichrome wire. Immediately slyf()87(a cs /oyqjh after the t8l(qf) 7os(/c j ahyysoaster is turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? b0 em4/p g)6ffrl/.(dey jxoaExplain.

Different lamps might ha lr270o+ca8lf46-kn sbkpnu vve batteries connected in either of the two arrangements s -f6cvok7+u 0r4 psn8knblla2hown in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How many e i8,daejf9 7eslectrons are flowing past any point in the wire per s,eds ea8 79fijecond?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7 A for 5.0 h. How much-pjrrk38s/g axq(k e9 charge passes through theg(xrqpr/kj -8 as3k e9 battery?    $ \times10^{ 5}\;C$

  What is the current in am;vtt .ikzqns7x ka98 xn;xp*,peres if $1200\,Na^+$ ions flow across a cell membrane in $3.5\mu s$? The charge on the sodium is the same as on an electron, but positive.    $ \times10^{-11 }\;A$

  What is the resistance of a toaster if 120 V prodh4s ujijn ex pok3t q)1400mh1uces a current of 4.2 A?    $\Omega$

  What voltage will produ a/7rh+1leqrt/mgnn j ;, 2pa/ef jm2bce 0.25 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A whelor330v3irs6h2 0pni2 fx5 ipmiiq; bn plugged into a 120-V line.
(a) What is its resistance?    $\Omega$
(b) How much charge passes through it in 15 min? (Assume direct current.)    $ \times10^{ 3}\;C$

  An electric clothes dryer has a hetb5m *jh3a )pdating element with a resistance of $9.6-\Omega$.
(a) What is the current in the element when it is connected to 240 V?    A
(b) How much charge passes through the element in 50 min?    $ \times10^{ 4}\;C$

  A 9.0-V battery is connec4wdl lkg*a 2aj*f +(,5yah tovted to a bulb whose resistance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electric transmission line carryik vtc4)0o ;;dcyjskqlj ernh (ja. -o7.eb11fng 2800 A (Fig. 18–34). The (jon-eh;t ca1 b;kj c7oqyk01rf s .4 dlvj.e)line has $2.5\times10^{ -5}\;\Omega$ resistance per meter, and the bird’s feet are 4.0 cm apart. What is the potential difference between the bird’s feet?    $ \times10^{-3 }\;V$

  An electric device draws 6.50 A a3g)dr5rkt pjss: h,4 w1ut)bse:kjt5t 240 V.
(a) If the voltage drops by 15%, what will be the current, assuming nothing else changes? $\approx$    A (retain one decimal places)
(b) If the resistance of the device were reduced by 15%, what current would be drawn at 240 V? $\approx$    A (retain one decimal places)

  A 12-V battery causes a current of 0.p2 u;ka u1fze/05av jt60 A through a resistor.
(a) What is its resistance, $\approx$    $\Omega$
(b) how many joules of energy does the battery lose in a minute?    J

  What is the diameter of a 1.00-m length of tungs ;j* j/oo/xwkyjp6t:mten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper wire 1.5 mm in d 4 r3eao)o3fuu 0r+kv6xqcu:jiameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10+ pfvo 8f2dh)h7q 9u-rrbboj*.0 m of aluminum wire 2.0 mm in diameter, to 20.0 m of copper wire 72 b9hp *)b -f r8juqhdor+ovf2.5 mm in diameter.   

  Can a 2.5-mm-diameter coppersop+*/r iqc/ *gs i(f:78drlj r ;aagu ;fx/ai wire have the same resistance as a tungsten wire of the same length? Give f :ar8f/s oug/+(7gr;rjl* aq /xcaidipi; s*numerical details.    mm

  A certain copper wirejum 7s+ hj9jklqx1n *d/ 3oor) has a resistance of $10.0\Omega$ At what point along its length must the wire be cut so that the resistance of one piece is 4.0 times the resistance of the other? What is the resistance of each piece?
$R_{short }$   $\Omega$
$R_{long }$    $\Omega$

  How much would you have to raise the temperature 727h4x+ npmkje6zodk of a copper wire (originally at7mjkx2n+e467kdo hzp $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same resis ouuh:;p) o7;d cj1jiotivity as tungsten does ato) ocj ju;1iup;h:od7 $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistao-xy/we fagd;./h is(x j 6bi*nce of about $12\Omega$ when cold ($20^{\circ}\,C$) and $140\Omega$ when on (hot). Estimate the temperature of the filament when hot assuming an average temperature coefficient of resistivity $\alpha\,=\,0.0060(C?)^{-1}$ .    $^{\circ}\,C$

  Compute the voltage drop along a +l96vc+z r(xsan7 bd-70 k2zzymnqsp26-m length of household no. 14 copper wire (used in 15-A circuits). The wire has diameter 1.628 mm and carries a 12-A current. l7vacpb rsk(z 6+nzynx-7+ 90sqmdz 2    V

  A rectangular solid made of carbon has sides of lengths 1.0 cm, 2njz s1/ n+yrp1.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine the rj+ynz/snpr1 1esistance for current that passes through the solid in
(a) the x direction,    $ \times10^{ -4}\;\Omega$
(b) the y direction,    $ \times10^{ -3}\;\Omega$
(c) the z direction. Assume the resistivity is $\rho\,=\,3.0\times10^{ -5}\;\Omega\cdot m$.
   $ \times10^{ -3}\;\Omega$

  Two aluminum wires have the same resistance. If one has twice the lenlp *2*g jnfk7q4 *foptgth of the other, what is the ratio of the diameter of the longer wire to t *2lk*o7fjt fpgpn* 4qhe diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precisi 2wi sfla7up5 -l 8d lh(c6b4xksknv48on 10.00-V power supply, and a currsi4- c58 2kavf4dsbw l 7k l8pn(hlxu6ent of 0.4212 A is precisely measured at 20.0$^{\circ}\,C$. The wire is placed in a new environment of unknown temperature where the measured current is 0.3618 A. What is the unknown temperature?    $^{\circ}\,C$

  A 10.0-m length of wire consists of 5.0 m of coppejk*wp)e;j dx4xgo ) b(r followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage difgp)k*(b4 dew jojx; x)ference of 85 mV is placed across the composite wire.
(a) What is the total resistance (sum) of the two wires? $\approx$    $\Omega$(retain two decimal places)
(b) What is the current through the wire?    A(retain two decimal places)
(c) What are the voltages across the aluminum part and across the copper part?
$V_{Cu}$    V(retain three decimal places)
$V_{Al}$    V(retain three decimal places)

  For some applications, it is important th.paxbwd/ rwn- eueo)irs:*01at the value of a resistance not change with temperature. For example, supp: de0*w.br 1)a/siurop-ewx nose you made a $4.70-k\Omega$ resistor from a carbon resistor and a Nichrome wire-wound resistor connected together so the total resistance is the sum of their separate resistances. What value should each of these resistors have (at 0$^{\circ}\,C$) so that the combination is temperature independent?
$R_{0C}$   $\Omega$
$R_{0N}$   $\Omega$

  The heating element of an electric oven is designed to produce 3.3 kW of heat whu 1gv*y ;d v)j(i5hrilen connected to a 240-V source. What must be the resistance o rv(5i;hu g1*)idyljv f the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD p05 y ;mgxpg u.d)pv w*/2kilexlayer that draws a/)idguy.5x g;wvplp e0km2 * x maximum of 320 mA of current?    W

  What is the maximum voltage tha7zdv u) a:nfjgou/jt7r m/5g ,t can be applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance ofg. .nf)l+z(yj3 koafc, and current through, a 75-W lightbulb connected to its proper source voltage n.koj a) (lzf .3yfcg+of 120 V.
   $\Omega$
   A
(b) Repeat for a 440-W bulb.
   $\Omega$
$\approx$    A(retain one decimal places)

  A 115-V fish-tank heater is rated at 110 W. Calcuwe :xbrwbh :tyzf:oolo11,e *5 jb*vaf4a;+jlate
(a) the current through the heater when it is operating,    A
(b) its resistance?    $\Omega$(Round to the nearest integer)

  A 120-V hair dryer has two settings: 850 W andds,-kca 6yu67kfo ol1 1250 W.
(a) At which setting do you expect the resistance to be higher? After making a guess, determine the resistance at
(b) the lower setting;    $\Omega$
(c) the higher setting.    $\Omega$

  You buy a 75-W lightbulb in Europe, where electricity fhu9r x3l z7c;is delivered to homes at 240 V. If you use the lightbulb in the United States at 120 V (assume its resistance does not change), how bright willrf9czx73lh; u it be relative to 75-W 120-V bulbs? [Hint: assume roughly that brightness is proportional to power consumed.]    as bright

  How many kWh of energy does a 550-W th3* hppk.c;mfv79 b re) fid7joaster use in the morning if it is in operation for pm7 v7dr.c3p )bih;*9ke fjhf a total of 15 min? At a cost of $9.0\,cents/kWh$, estimate how much this would add to your monthly electric energy bill if you made toast four mornings per week.
energy $\approx$    kWh
cost $\approx$    cents/mouth

  At 0.095 dollars per kWh, what does it c0nr 5wq:ln-woost to leave a 25-W porch light on day and nighwn :- l05onqrwt for a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connected in series 0h9qf,gbq+-i :b: 5z u dtmk*ht agz*oas in Fig. 18–4b (Fig. 18–36). The b: qhu a 0gt h:gbzmf*+i9k5,d- obtzq*ulb draws 450 mA when turned on.
(a) Calculate the resistance of the bulb and the power dissipated.
$\approx$    $\Omega$(retain one decimal places)
   W
(b) By what factor would the power increase if four D-cells in series were used with the same bulb? (Neglect heating effects of the filament.) Why shouldn’t you try this?   

  What is the total amount of energy stored iy1fl, -ribmquc e334z n a 12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulb6b ed8+w(lv3 lfwcioki2n,h3 s, connected to 120 V as in Fig. 18–20, can be used without chdkl 33 i8( we2lwnf6+ibov, blowing a 15-A fuse?    bulbs

  An extension cord made of two wires of diameter 0.129 cm (no. 16 copper wire)m9;7qyx57 jtcbcw r.w4 fwjv;zt ;ab+ and of length 2.7 m (9 ft) is connected to an electric heater which draws 15.0 A on a 120-V line. How much power is dissipated in the b;w7 qjc9x. 7 v5jfzbamwc;w4+t r;ty cord?    W

  A power station delivers 620 kW of power at 12,000 V .)qax(+u grye4t .tcy ux 7y3ato a factory through wires with total resig reaxx. 73cu.q y y+)4y(ttuastance $3.0\Omega$ How much less power is wasted if the electricity is delivered at 50,000 V rather than 12,000 V?    $ \times10^{ 3}\;W$

  The current in an electromagnet connected to a 240-V line is 17.5 A. At0ss0a9bofxrs mg u- .06dzn /u what rate must cooling water pass over the coils if the water temperatmu0d00saux srnsg .b -f/69oz ure is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a car to heat a cup of water fonbjv8 /vr)yx.r coffee or tea. If the hvy)jv8x r/ nb.eater can heat 120 mL of water from 25$^{\circ}\,C$ to 95$^{\circ}\,C$ in 8.0 min,
(a) approximately how much current does it draw from the car’s 12-V battery, $\approx$    A(Round to the nearest integer)
(b) what is its resistance? Assume the manufacturer’s claim of 60% efficiency.    $\Omega$

  Calculate the peak ce1fmy3q. el)qurrent in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 V, is across g.9u jyvtn we .u)on.1:;hs5(wpzehl a $330-\Omega$ resistor. What are the rms and peak currents in the resistor?
$I_{peak}$$\approx$    A(retain two decimal places)
$I_{rms}$ =    A

  Estimate the resistance of sug c+w1/;3h:jmqrzcthe $120-V_{rms}$ circuits in your house as seen by the power company, when
(a) everything electrical is unplugged,
(b) there is a lone 75-W lightbulb burning.    $\Omega$

  The peak value of an alternating current in a 1500-Wqp)t)*kt +*z . vdnbt-xte+gz device is 5.4 A. What is the rms voltage ac-+ xtt bd*v) nzztek)gt.q+* pross it?    V (Round to the nearest integer)

  An 1800-W arc welder is connecei3/52 dqlte)n ju1al ted to a $660-V_{rms}$ ac line. Calculate
(a) the peak voltage$\approx$    V(retain one decimal places)
(b) the peak current.    A

  (a) What is the maximum instantaneous power dissipated by a 7u0eokg( ::gwb) vv e)qb5hjc 3.0-hp pump connected 7ekcg)gjo) 0(b vwb:h:q vu5eto a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected to a n bur5)n9 z*rx$240-V_{rms}$ ac line has a resistance of $34\Omega$.
(a) What is the average power used?    W
(b) What are the maximum and minimum values of the instantaneous power?
$P_{max}$    W
$P_{min}$    W

  A 0.65-mm-diameter copper wire ca siloh(;f0) ntp+(ncarries a tiny current of $2.3\mu A$. What is the electron drift speed in the wire?    $ \times10^{-10 }\;m/s$

  A 5.80-m length of 2.0-mm-diameter wire carries a 750-mA current)hgui,lu*p ;jcbgu1 9 when 22.0 mV is applied to its ends. If the dr*jg;cu)u1p ih9lgb,u ift speed is $ 1.7\times10^{-5 }\;m/s$, determine
(a) the resistance R of the wire, $\approx$    $\Omega$(retain three decimal places)
(b) the resistivity $\rho$.    $ \times10^{-8 }\;\Omega\cdot m$
(c) the number n of free electrons per unit volume.    $ \times10^{28 }\;e^-/m^3$

  At a point high in the Earth’s atmosphzg7k4d46j )le b)e 6oq*jjowh ere, $He^{2+}$ ions in a concentration of $ 2.8\times10^{12 }\;/m^3$ are moving due north at a speed of $ 2.0\times10^{6 }\;m/s$. Also, a $ 7.0\times10^{11 }\;/m^3$ concentration of ${O_2}^-$ ions is moving due south at a speed of $ 7.2\times10^{6 }\;m/s$. Determine the magnitude and direction of the net current passing through unit area $(A/m^2)$.    $A/m^2$  ----待选择----NorthSouth 

  At a point high in the Earth’s atmo: v. )nv0nnve 7-9xl sd+psxjlsphere, $He^{2+}$ ions in a concentration of $ 2.8\times10^{12 }\;/m^3$ are moving due north at a speed of $ 2.0\times10^{6 }\;m/s$. Also, a $ 7.0\times10^{11 }\;/m^3$ concentration of ${O_2}^-$ ions is moving due south at a speed of $ 7.2\times10^{6 }\;m/s$. Determine the magnitude and direction of the net current passing through unit area $(A/m^2)$.    $A/m^2$  ----待选择----NorthSouth 

  What is the magnitude of the electricao)n)(p6w )ame c/ekc field across an axon membrane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated with a3evezx +bx/:1lj jw+a ,c+ kvpn electric pulse. The action potential is detected at a point 3.40 cm down the axon 0.0052 s later. When the action potential is detected 7.20 cm from the point of stimulation, the time j+/:+a xv3,bcl jekx pevzw1+ required is 0.0063 s. What is the speed of the electric pulse along the axon? (Why are two measurements needed instead of only one?)    m/s

  Estimate how much energy isstg( s f3 jp/bw8uvn4lq0 2 lh2/l:zrm required to transmit one action potential along the axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent t22wsnv4tbus lm(ll /3 qfrgp:0h 8j/zo the energy stored by charging the axon capacitance; see Section 17–9]. What minimum average power is required for $10^4$ neurons each transmitting 100 pulses per second?
E =    $ \times10^{-11 }\;J$
P =    $ \times10^{-5 }\;W$

  During an action potential,lh m ;pr7)p iloaat9c7 lw2o00 $Na^+$ ions move into the cell at a rate of about $3 \times10^{-7 }\;mol/m^2\cdot s$. How much power must be produced by the “active $Na^+$ pumping” system to produce this flow against a $+30-Mv$ potential difference? Assume that the axon is 10 cm long and $20\mu m$ in diameter.    $ \times10^{-9 }\;W$

  How many coulombs are there in 1.0 j3 - dw3,h2oai0eegsk0 ampere-hour?    C

  What is the average current drawn by a j/;o*/fvui9n vr4 ygy 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights o z1 z97ishjq-xn. If each of the two headlights uses 40 W and each of the two9izzh1 sj7 q-x taillights 6 W, for a total of 92 W, how long will a fresh 12-V battery last if it is rated at $95A\cdot h$? Assume the full 12 V appears across each bulb.    h

  The heating element of a 110-V, 1500-W heater is6x f 6iwo uj344ri2iyl 5.4 m long. If it is made of iron, what must its diameyfirj3 w4o x66 u4l2iiter be?    $ \times10^{ -4}\;m$

  The conductance G of an obisfwi)a4 / 3 gz-r3bkpject is defined as the reciprocal of the resistance R; tka3w fbs-i)pz4/i g3r hat is, $G\,=\,1/R$. The unit of conductance is a mho $(=ohm^{-1})$, which is also called the siemens (S). What is the conductance (in siemens) of an object that draws 730 mA of current at 3.0 V?    S

  A small city requires about 10 MW of power. Sq;zzc.0(lu * rfkqc+uuppose that instead of using high-voltage lines to supply the power, the power is delivered at 120 V. Assuming a two-wire line of 0.50-cm-diameter copper wire, estimate the cost of the energy lost to heat per hour per(zcqkl qf 0z+*u .r;cu meter. Assume the cost of electricity is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular household uses a 1.8-kW heo ,zs,5z7.s ovmy v5seater $3.0 h/day$ (“on” time), four 100-W lightbulbs $6.0 h/day$, a 3.0-kW electric stove element for a total of $1.4 h/day$ and miscellaneous power amounting to $2.0 kWh/day$. If electricity costs $0.105 per kWh, what will be their monthly bill (30 d)?    dollars per month
(b) How much coal (which produces $7000 kcal/kg$) must be burned by a 35%-efficient power plant to provide the yearly needs of this household?    kg of coal

A length of wire is cut in half and the two lengths a3n2jiabycwt 3 u*i1o3re wrapped together side by side to make a thicker wire. How does the resistance of this new combinat3ui *i 2bya1j 3co3nwtion compare to the resistance of the original wire?

  A 1200-W hair dryer is designed for 114sp :4sjfxaxe ck v.m,ggn;0 57 V.
(a) What will be the percentage change in power output if the voltage drops to 105 V? Assume no change in resistance.    % decrease
(b) How would the actual change in resistivity with temperature affect your answer?

  The wiring in a house must be thick enough so it does not become so ho)9:6 g oprximvm ye puvpf .(t/fs+3-st as to start a fire. What diameter must a copper wire be if it is to ca-xyp(o 6m t9guf 3vm /p.rsve)+fis:prry a maximum current of 35 A and produce no more than 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is given by the equat5lxn ;2az,n8rcantwyv4, h ;lion $I\,=\,1.80sin210t$, where I is in amperes and t in seconds.
(a) What is the frequency?    Hz
(b) What is the rms value of the current?    A
(c) If this is the current through a $42-\Omega$ resistor, write the equation that describes the voltage as a function of time. (  sin 210 t)V

  A microwave oven running at 65% efficiency delivers 950 W of energy ad,h)c9h44da1msvyef b ff):per second to the interior. Fis1f):fbedadm9 ) 4h4v cf ,ayhnd
(a) the power drawn from the source,    W
(b) the current drawn. Assume a source voltage of 120 V.    A

  A $1.00-\Omega$ wire is stretched uniformly to 3.00 times its original length. What is its resistance now?    $\Omega$

  220 V is applied to two different conductors made of the same m0rho sw.7gji ;aterial. One conducrhi;w.og 7s 0jtor is twice as long and twice the diameter of the second. What is the ratio of the power transformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is usi 4c5+lkya* sfd-eh,j ed to heat a room of volume $62\,m^3$ Air is brought into the room at 5$^{\circ}\,C$ and is completely replaced twice per hour. Heat loss through the walls amounts to approximately $850 kcal/h$. If the air is to be maintained at 20$^{\circ}\,C$, what minimum wattage must the heater have? (The specific heat of air is about $0.17 kcal/kg\cdot C?$)    W

  A 2200-W oven is hooked+d orlbwtn6/0 to a 240-V source.
(a) What is the resistance of the oven?    $\Omega$
(b) How long will it take to bring 120 mL of 15$^{\circ}\,C$ water to 100$^{\circ}\,C$ assuming 75% efficiency?    s
(c) How much will this cost at $11 cents/kWh?$    cents

  A projected electric vehicle makes use of storage batteries as its source of enep m4jeoq*6wr- rgy. Itrm4q*o6 w-epj s mass is 1560 kg and it is powered by 24 batteries, each 12 V, $95A\cdot h$. Assume that the car is driven on level roads at an average speed of $45 km/h$ and the average friction force is 240 N. Assume 100% efficiency and neglect energy used for acceleration. No energy is consumed when the vehicle is stopped, since the engine doesn’t need to idle.
(a) Determine the horsepower required.    hp
(b) After approximately how many kilometers must the batteries be recharged?    km

  A $12.5-\Omega$ resistor is made from a coil of copper wire whose total mass is 18.0 g. What is the diameter of the wire, and how long is it?
L =    m
A =    $ \times10^{-4 }\;m$

  A 100-W, 120-V lightbulb has a resistance i0 lhp37wb5 yj*;eq rcof $12\Omega$ when cold (20$^{\circ}\,C$) and $140\Omega$ when on (hot). Calculate its power consumption at
(a) the instant it is turned on,    W
(b) after a few moments when it is hot.    W

  The Tevatron accelerator at Fermilab (Illinois) is designed tj.+9/lfucs *i 1)i,xp5okzj+tilkw mo carry an 11-mA beam of protons travu1tji*lsk9/ cl+z )pi i.,+ofmx5wkjeling at very nearly the speed of light ($ 3.0\times10^{8 }\;m/s$) around a ring 6300 m in circumference. How many protons are stored in the beam?    $ \times10^{12 }\;protons$

  An air conditioner draws 12 A at 220-V ac. The connecting cord isrz1efgn ,n(ler pb//69 ef /ar copper wire with a diameter 96panfe /frbeg1l/ r/nez,(rof 1.628 mm.
(a) How much power does the air conditioner draw?    W
(b) If the total length of wire is 15 m, how much power is dissipated in the wiring? $\approx$   W(Round to the nearest integer)
(c) If no. 12 wire, with a diameter of 2.053 mm, was used instead, how much power would be dissipated? $\approx$   W(Round to the nearest integer)
(d) Assuming that the air conditioner is run 12 h per day, how much money per month (30 days) would be saved by using no. 12 wire? Assume that the cost of electricity is 12 cents per kWh. $\approx$   cents per month (Round to the nearest integer)

  A fish-tank heater is rated at 95 W when connected to 120 V. The heating elemo:bkeu+obyhr y ad vu0jdh 66o3u;4 51ent is a coil y; d3:ou jv6uurdb6ohe +4k01h5oabyof Nichrome wire. When uncoiled, the wire has a total length of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies frfc1dl, ,giz,h:d( paaom about 12 V when the car is off to about 13.8 V pdzf :1l gcda,ih a,,(when the car is on and the charging system is in operation, a difference of 15%. By what percentage does the power delivered to the headlights vary as the voltage changes from 12 V to 13.8 V? Assume the headlight resistance remains constant.    % increase

  Lightbulb A is rated at 120 V and 40 W for household applicationsxqww9 g,bkx /a0c*bal3z d0y3 . Lightbulb B is ,x0qb0 a 3wywc/3xak*9z gdblrated at 12 V and 40 W for automotive applications.
(a) What is the current through each bulb? $I_A$ =    A $I_B$ =    A
(b) What is the resistance of each bulb? $R_A$ =  $\Omega$ $R_B$ =  $\Omega$
(c) In one hour, how much charge passes through each bulb? $Q_A$ =    C$Q_B$ =    C
(d) In one hour, how much energy does each bulb use?    $ \times10^{5 }\;J$
(e) Which bulb requires larger diameter wires to connect its power source and the bulb?  ----待选择----Bulb BBulb A 

  Copper wire of diameter 0.259 cm is used t4z kpm uybh35,o connect a set of appliances at 120 V, which draw 2250 W of power 5uhy4 zpbmk 3,total.
(a) What power is wasted in 25.0 m of this wire?    W
(b) What is your answer if wire of diameter 0.412 cm is used?    W

  A copper pipe has an i75wz,zpna5 8le -caplnside diameter of 3.00 cm and an outside diameter of 5.00 cm (Fig. 18–37). What is the resistance7-,e5 zp a aplc5wz8ln of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that its length dk7ystk0 n n1azr 4va+sz )t2e9oubles, by what factor does the power dissipated in the wire change, assuming it remains hooked up to the same voltage souks 9nr7+)k02 avs1 azntyet4zrce?

  A tungsten filament used in a0bb ea.xh x*yw 7.q(xt flashlight bulb operates at 0.20 A and 3.2 V. If its resistancee*a xx0tb( b7y. xqwh. at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$